Water is frequently used to transport unwanted materials—waste—to a facility where the waste is removed or neutralized in the water. For example, water carries most sewage and industrial waste, such as chemicals, in the form of wastewater to a treatment facility where the water is treated and then returned to the environment for future use. The wastewater treatment process typically includes three general phases. The first phase, or primary treatment, involves mechanically separating the dense solids in the wastewater from the less dense solids and liquid in the wastewater. This is typically done in sedimentation tanks with the help of gravity. The second phase, or secondary treatment, involves the biological conversion of carbonaceous and nutrient material in the wastewater to more environmentally friendly forms. This is typically done by promoting the consumption of the carbonaceous and nutrient material by bacteria and other types of beneficial organisms already present in the wastewater or mixed into the wastewater. The third phase, or tertiary treatment, involves removing the remaining pollutant material from the wastewater. This is typically done by filtration and/or the addition of chemicals and/or UV light and/or Ozone to neutralize harmful organisms and/or remove pollutant material.
The second phase of the wastewater treatment process typically includes an aerobic—with oxygen—portion in which bacterial and other microorganisms are provided dissolved oxygen to promote their consumption of the carbonaceous and nutrient materials, and an anoxic—oxygen from a nitrate/nitrite source—portion in which the bacteria and other microorganisms use the oxygen in the nitrate/nitrite for their metabolic functions. The second phase may also include an anaerobic—without oxygen—portion in which bacteria and other microorganisms metabolically function without oxygen. The aerobic, anoxic and anaerobic portions are typically carried out in tanks that are divided into aerobic, anoxic and anaerobic zones. The tank may include one zone in which the aerobic portion operates and one in which the anoxic portion operates and one in which the anaerobic portion operates, or the tank may include any combination of any number of these zones. In some applications, a tank may be solely dedicated to one of the three aerobic, anoxic and anaerobic portions.
In the aerobic process, wastewater that includes ammonium (NH4) and organic waste containing nitrogen, for example Urea ((NH2)2CO), enters the aerobic zone. In the presence of dissolved oxygen (O2), bacteria and other microorganisms convert the ammonium into nitrate (NO3) via nitrite (NO2). The nitrate can then be anoxically processed into nitrogen gas (N2), which is harmless in the environment. A blower and diffusers supply the dissolved oxygen to the wastewater. The blower provides air to the diffusers, and the diffusers generate and release tiny bubbles so that the oxygen in the bubbles will dissolve in the wastewater. As the aerobic process progresses, the amount of ammonium in the wastewater decreases while the amount of nitrate and dissolved oxygen increases. The amount of dissolved oxygen increases because the demand for the dissolved oxygen decreases as the amount of nitrate increases. After most of the ammonium has been converted into nitrate, the wastewater is ready to be anoxically processed.
In the anoxic process, wastewater that includes nitrate and the organic waste containing nitrogen enters the anoxic zone. In the absence of dissolved oxygen, bacteria and other microorganisms convert the nitrate into nitrogen gas and the organic waste containing nitrogen into ammonium. As the anoxic process progresses, the amount of nitrate decreases and the amount of ammonium increases. After most of the nitrate has been converted into nitrogen gas, the wastewater is ready to be aerobically processed or treated in the tertiary treatment phase.
Mixing the contents in each of the aerobic and anoxic zones promotes the conversion reactions in each zone by increasing the contact of the components, such as the dissolved oxygen (aerobic zone), nitrite/nitrate (anoxic zone), wastewater, and bacteria and other microorganisms, with the other components in each zone. In the aerobic zone, the wastewater is typically mixed by the movement of the tiny bubbles through the wastewater and a mechanical mixer that includes a screw or blade that is turned by a motor. In the anoxic zone, a mechanical mixer typically only mixes the wastewater because the anoxic process requires little or no dissolved oxygen, which the tiny bubbles from the diffusers provide.
The typical prior art means for mixing the wastewater in the aerobic and anoxic zones is subject to several limitations. Mixing the aerobic zone with the movement of the tiny bubbles through the wastewater requires a substantial amount of tiny bubbles to be injected into the wastewater to sufficiently mix the wastewater. Disadvantageously, the demand for dissolved oxygen in the wastewater may decrease to the point where the amount of tiny bubbles injected into the wastewater to satisfy the demand would not be enough to sufficiently mix the wastewater. When this happens the amount of tiny bubbles injected into the wastewater is typically kept high enough to sufficiently mix the wastewater. Thus, the diffusers consume more power than required to oxygenate the wastewater and can inject more dissolved oxygen into the aerobic zone than required.
Mixing the aerobic and anoxic zones with a mechanical mixer consumes a large amount of power relative to the amount of wastewater that it mixes, and often mixes some, but not all, of the wastewater in each zone. Thus, some of the sludge in the aerobic and anoxic zones remains on the bottom of the tank after it settles there. In the aerobic zone, the settled sludge can plug some of the diffusers. This can reduce the amount of dissolved oxygen injected into the wastewater, and thus requires one to clear the plugged diffusers.